311 research outputs found
Unimodular metagravity vs. General Relativity with a scalar field
The unimodular metagravity, with the graviscalar as a dark matter, is
compared with General Relativity (GR) in the presence of a scalar field. The
effect of the graviscalar on the static spherically symmetric metric is
studied. An exact limit solution representing a new cosmic object, the
(harmonic) graviscalar black hole, is given. The relation with the black hole
in the environment of a scalar field in GR is discussed.Comment: 7 pages. Report presented at the RAS Conference "Physics of
Fundamental Interactions", Protvino, December 22-25, 200
Molecular line and continuum study of the W40 cloud
The dense cloud associated with W40, one of the nearby H II regions, has been
studied in millimeter-wave molecular lines and in 1.2 mm continuum. Besides,
1280 MHz and 610 MHz interferometric observations have been done. The cloud has
complex morphological and kinematical structure, including a clumpy dust ring
and an extended dense core. The ring is probably formed by the "collect and
collapse" process due to the expansion of neighboring H II region. Nine dust
clumps in the ring have been deconvolved. Their sizes, masses and peak hydrogen
column densities are: pc, and cm, respectively. Molecular lines are observed
at two different velocities and have different spatial distributions implying
strong chemical differentiation over the region. The CS abundance is enhanced
towards the eastern dust clump 2, while the NH, NH, and
HCO abundances are enhanced towards the western clumps. HCN and
HCO do not correlate with the dust probably tracing the surrounding gas.
Number densities derived towards selected positions are: cm. Two western clumps have kinetic temperatures 21 K and 16 K and
are close to virial equilibrium. The eastern clumps 2 and 3 are more massive,
have higher extent of turbulence and are probably more evolved than the western
ones. They show asymmetric CS(2--1) line profiles due to infalling motions
which is confirmed by model calculations. An interaction between ionized and
neutral material is taking place in the vicinity of the eastern branch of the
ring and probably trigger star formation.Comment: 16 pages, 6 figure
Markov Process of Muscle Motors
We study a Markov random process describing a muscle molecular motor
behavior. Every motor is either bound up with a thin filament or unbound. In
the bound state the motor creates a force proportional to its displacement from
the neutral position. In both states the motor spend an exponential time
depending on the state. The thin filament moves at its velocity proportional to
average of all displacements of all motors. We assume that the time which a
motor stays at the bound state does not depend on its displacement. Then one
can find an exact solution of a non-linear equation appearing in the limit of
infinite number of the motors.Comment: 10 page
On Spin Systems with Quenched Randomness: Classical and Quantum
The rounding of first order phase transitions by quenched randomness is
stated in a form which is applicable to both classical and quantum systems: The
free energy, as well as the ground state energy, of a spin system on a
-dimensional lattice is continuously differentiable with respect to any
parameter in the Hamiltonian to which some randomness has been added when . This implies absence of jumps in the associated order parameter, e.g.,
the magnetization in case of a random magnetic field. A similar result applies
in cases of continuous symmetry breaking for . Some questions
concerning the behavior of related order parameters in such random systems are
discussed.Comment: 8 pages LaTeX, 2 PDF figures. Presented by JLL at the symposium
"Trajectories and Friends" in honor of Nihat Berker, MIT, October 200
W40 region in the Gould Belt : An embedded cluster and H II region at the junction of filaments
We present a multiwavelength study of W40 star-forming region using IR
observations in UKIRT JHK bands, Spitzer IRAC bands & Herschel PACS bands; 2.12
micron H2 narrow-band imaging; & radio observations from GMRT (610 & 1280 MHz),
in a FoV of ~34'x40'. Spitzer observations along with NIR observations are used
to identify 1162 Class II/III & 40 Class I sources in the FoV. The NN stellar
surface density analysis shows that majority of these YSOs constitute the
embedded cluster centered on the source IRS1A South. Some YSOs, predominantly
younger population, are distributed along & trace the filamentary structures at
lower stellar surface density. The cluster radius is obtained as 0.44pc -
matching well with the extent of radio emission - with a peak density of
650pc^-2. The JHK data is used to map the extinction which is subsequently used
to compute the cloud mass. It has resulted in 126 Msun & 71 Msun for the
central cluster & the northern IRS5 region, respectively. H2 narrow-band
imaging displays significant emission, which prominently resembles fluorescent
emission arising at the borders of dense regions. Radio analysis shows this
region as having blister morphology, with the radio peak coinciding with a
protostellar source. Free-free emission SED analysis is used to obtain physical
parameters of the overall region & the IRS5 sub-region. This multiwavelength
scenario is suggestive of star formation having resulted from merging of
multiple filaments to form a hub. Star formation seems to have taken place in
two successive epochs, with the first epoch traced by the central cluster & the
high-mass star(s) - followed by a second epoch which is spreading into the
filaments as uncovered by the Class I sources & even younger protostellar
sources along the filaments. The IRS5 HII region displays indications of
swept-up material which has possibly led to the formation of protostars.Comment: 17 pages, 12 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Multi-frequency Studies of Massive Cores with Complex Spatial and Kinematic Structures
Five regions of massive star formation have been observed in various
molecular lines in the frequency range GHz. The studied regions
possess dense cores, which host young stellar objects. The physical parameters
of the cores are estimated, including kinetic temperatures ( K),
sizes of the emitting regions ( pc), and virial masses (). Column densities and abundances of various molecules are
calculated in the local thermodynamical equilibrium approximation. The core in
99.982+4.17, associated with the weakest IRAS source, is characterized by
reduced molecular abundances. Molecular line widths decrease with increasing
distance from the core centers (). For b\ga 0.1~pc, the dependences
are close to power laws (), where varies from
to , depending on the object. In four cores, the
asymmetries of the optically thick HCN(1--0) and HCO(1--0) lines indicate
systematic motions along the line of sight: collapse in two cores and expansion
in two others. Approximate estimates of the accretion rates in the collapsing
cores indicate that the forming stars have masses exceeding the solar mass.Comment: 18 pages, 7 figures, 6 table
A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high
signal-to-noise ratios toward distinct positions in three selected objects in
order to search for small-scale structure in molecular cloud cores associated
with regions of high-mass star formation. In some cases, ripples were detected
in the line profiles, which could be due to the presence of a large number of
unresolved small clumps in the telescope beam. The number of clumps for regions
with linear scales of ~0.2-0.5 pc is determined using an analytical model and
detailed calculations for a clumpy cloud model; this number varies in the
range: ~2 10^4-3 10^5, depending on the source. The clump densities range from
~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps
are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump
gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal
energy of the gas in the model clumps is much higher than their gravitational
energy. Their mean lifetimes can depend on the inter-clump collisional rates,
and vary in the range ~10^4-10^5 yr. These structures are probably connected
with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table
Chemical differentiation in regions of high-mass star formation I. CS, dust and N2H^+ in southern sources
Aims. Our goals are to compare the CS, N2H+ and dust distributions in a
representative sample of high-mass star forming dense cores and to determine
the physical and chemical properties of these cores. Methods. We compare the
results of CS(5-4) and 1.2 mm continuum mapping of twelve dense cores from the
southern hemisphere presented in this work, in combination with our previous
N2H+(1-0) and CS(2-1) data. We use numerical modeling of molecular excitation
to estimate physical parameters of the cores. Results. Most of the maps have
several emission peaks (clumps). We derive basic physical parameters of the
clumps and estimate CS and N2H+ abundances. Masses calculated from LVG
densities are higher than CS virial masses and masses derived from continuum
data, implying small-scale clumpiness of the cores. For most of the objects,
the CS and continuum peaks are close to the IRAS point source positions. The
CS(5-4) intensities correlate with continuum fluxes per beam in all cases, but
only in five cases with the N2H+(1-0) intensities. The study of spatial
variations of molecular integrated intensity ratios to continuum fluxes reveals
that I(N2H+)/F{1.2} ratios drop towards the CS peaks for most of the sources,
which can be due to a N2H+ abundance decrease. For CS(5-4), the I(CS)/F{1.2}
ratios show no clear trends with distance from the CS peaks, while for CS(2-1)
such ratios drop towards these peaks. Possible explanations of these results
are considered. The analysis of normalized velocity differences between CS and
N2H+ lines has not revealed indications of systematic motions towards CS peaks.Comment: 13 pages, 5 figures, accepted by Astronomy and Astrophysic
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